. >>> president obama will be traveling to boston on thursday to attend an interfaith service for the victims. evidence is painstaking work. they are looking for every last shred of the two devices across the crime scene that spans blocks. this is the first look at what one of the bombs might have looked like before it went off. and they show a bag next to a box in the crowd and after it's come back the explosion that is gone. apparently they are easy to build. >> at least one of the bombs was inside an appliance you might have in your kitchen but hidden in the backpack. investigators found a circuit board that they believed was used as a detonator. >> this gives us the first look at a deadly device. a mangled pressure cooker that was laced with nails, ball bearings and bbs. it's clear the intent was maximum damage. >> you are adding the ability to injure people, kill, maim, and those projectiles become like bullets. >> the bombs were hidden inside a black nylon backpacks and inside pressure cookers. an issue in a jihad the magazine, there was a chapter called to make a bomb in the ki